1. Field of the Invention.
The present invention relates to corrosion resistant magnetic surfaces. In particular, it relates to corrosion resistant magnetic head assemblies of the type used to record and read data, and a method for protecting the exposed magnetic surfaces of the heads.
2. Description of the Prior Art.
Magnetic metal alloys such as permalloy are commonly used as one of the materials for forming magnetic head assemblies used in computer data storage devices. It is known in the art that the magnetic surfaces of magnetic head assemblies are attacked by moisture and chemicals causing corrosion, which reduces the reliability and accuracy of the head, and can lead to total disc drive failure. This corrosion most commonly occurs after manufacture but before use.
Permalloy is a magnetic nickel-iron alloy which has excellent magnetic properties, but which is subject to corrosion. In particular, vaporized water, chlorides and sulfides are known to corrode permalloy. Other magnetic alloys are also susceptible to corrosion.
Magnetic head assemblies typically include a plurality of exposed magnetic surfaces, such as pole tips at or on the air bearing surface of the "flying head" assembly, for example. The air bearing surfaces for purposes of this disclosure are the surfaces of the magnetic recording head which contact the magnetic recording media when the magnetic recording media is not in motion. Frictional contact between the magnetic portions of the air bearing surfaces generated during starting and stopping prevents further corrosion.
The fly height for purposes of this application is defined as the distance between the surface of the magnetic recording media, and the air bearing surface of the magnetic recording head. A coating applied to the air bearing surface of the head increases the fly height, which reduces the signal amplitude. Minimizing the fly height assures that the signal sent to and from the magnetic head has minimum distortion, has the maximum accuracy. The aim of the industry is to achieve a higher density of magnetic transitions in the recording media. This is accomplished in part by reducing fly heights.
Although it is known in the art generally that the air bearing surface of a magnetic head can be coated with a layer of anticorrosive material, it has been undesirable before the present invention, for a variety of reasons, to coat magnetic pole tips in magnetic heads with any substance.
For example, the Head et al U.S. Pat. No. 4,130,847 discloses the application of a thin layer of film applied to the air bearing surface of a transducer, including the pole tips for corrosion and wear protection. The thin layer is preferably formed from chromium. It is known that the application of a layer of coating to the surface of pole tips adversely affects the magnetic properties of the transducer. In particular, the magnetic field is weakened, and the signal generated in the transducer is distorted, compared to a signal generated by a transducer without a pole tip coating.
Plotto U.S. Pat. No. 4,327,387 discloses a magnetic head slider assembly having a body supporting a transducer. The transducer reads and writes information contained in a data carrier. On the surface of the transducer facing the surface of the data carrier is a lubricating layer, preferably formed from an organic monomolecular polar compound. The preferred lubricating layer is formed from methyl (CH.sub.3 --) groups. The layer is between about 30 and 50 Angstroms in thickness, and increases the fly height by that amount. Increases in fly height are known to decrease the signal amplitude of the transducer.
The aim of the industry is to reduce fly heights as much as possible in order to increase the accuracy of data transfer to and from high density recording media. High density recording media generally spins at a faster rate.
With decreased fly heights, it is imperative that no foreign substances (such as coatings) be present on the transducer surface or the recording media surface which are subject to peeling or flaking. Particulates located between the transducer surface and the recording media are known to cause hard drive crashes. For the above-mentioned reasons, the practice in the industry has been to prevent corrosion in pole tips by using other methods of protection, such as by preventing the exposure of the manufactured heads to corrosive environments.
One known method of preventing corrosion in manufactured magnetic heads includes storing and shipping the heads in contamination-free containers containing a desiccant. Another method includes storage of the component parts in a noncorrosive gaseous environment such as nitrogen. Still another method includes the storage of the magnetic heads in a vacuum-packaged, contamination free container.
Although the use of corrosion inhibiting coatings on magnetic components such as magnetic heads has not been considered desirable before the present invention, the application of corrosion inhibiting chemicals to metal surfaces is well known. For example, the article by Mateinzo et al., Organic Corrosion Inhibitors to Improve the Durability of Adhesion Between Aluminum and Polymeric Coatings, 22 American Chemical Society, p. 234 (1986) discloses the use of organosilanes as a corrosion inhibitor/bonding agent for aluminum surfaces. A mercaptosilane was selected as a preferred anticorrosive agent for aluminum.
The above-mentioned prior art references fail to disclose a method of protecting the magnetic surfaces of a magnetic head during the manufacture, storage and shipping of magnetic recording head assemblies. A temporary coating which does not permanently increase fly height, significantly reduces corrosion, does not distort the signal generated by the magnetic recording head, and does not increase the potential for catastrophic hard disc failure would therefore be very desirable.